Assessment of field sattelite-based positioning systems for reduced, more precise use of crop inputs.

End of Project ReportThe mapping of within-field crop yield variations offers a basis for the adjustment of input application rates to match yield potential. The aim of this project was to examine available yield mapping components and systems, and to assess the benefits that could accrue from yield mapping. The work also included site investigations of possible causes of yield reduction, and an evaluation of the potential increase in profitability from variable-rate N application. Yield mapping requires the continuous measurement of harvester position and grain yield. Accurate positioning was achieved with systems which received a remote correction signal via communications satellite. A grain flow meter in the clean grain elevator gave low errors in conditions where the deflector plate could be kept clean. The production of useful yield maps was sometimes limited by rainy weather leading to wet crops, lodging, and big variations in harvest conditions within the field. Difficulties are also presented by small, irregularly-shaped fields. The level of within-field variation in cereal yields (25% of the field area at least 21% below the mean) suggests that there is scope for identifying low-yielding areas and either taking corrective action or applying reduced inputs. An analysis of the results of N fertiliser trials suggests a potential gain from about £20/ha in sugar beet to less than £10/ha in spring barley if N application rate could be varied to apply the optimum amount to each area within a field. All the costs of application map development and variable-rate application would need to fall below these gains to justify the use of the technology. To allow further use to be made of yield maps, it is desirable that the factors responsible for yield reduction be identified, in particular those which recur each year. In the present study, soil chemical analysis and compaction affected yield in only a small proportion of cases. Differences between maps from successive years have been small. It is concluded that the immediate financial benefits from the use of this technology will be small. However, in a future where the recording, justification and minimisation of inputs such as pesticides and fertiliser will grow in significance, and where the cost of the equipment and software will continue to fall, yield mapping and variable-rate input application will find a useful role